Found this edition of the French programme Pop Deux, dated December 5th 1970. It starts with a recording of Woody Guthrie followed by live performances by Blodwyn Pig, Matthews Southern Comfort. The best is last: 30 minutes of Fairport Convention (after Sandy Denny left) with great work from Richard Thompson and Dave Swarbrick.
Just found this. Elvis Costello/Declan MacManus in his band Flip City in 1974 at a festival in London. Starts around 43.30 in. They play 2 songs, sounding very pub-rockish.